I assume Dan that the bushes you will get made are for your TM pens and possibly Phil's only and not for 90% of the rubbish that is out there. As your pens and Phil's Mistral are upmarket pens then surely you can have your tubes specified to a certain tolerance which should be honoured by whoever makes your kits. If that is the case then you could have mandrels specified to the same tolerance and also the bushes. As most turners use a mandrel saver then as long as your mandrel fits the saver with a close tolerance then the majority of the turners on this forum will be winners as they already buy your kits rather than kits from other suppliers.
As Woody says even if the bushes wear out then just replace them because at the end of the day a set of bushes are about the same price as a cup of coffee.
I would say go ahead with this idea and keep up the good work as I think you are on to a winner !!! 